1. Field of the Invention
This invention relates to a track rail fixing structure for a linear motion unit in which a casing-carrying slider is formed so that the slider can be moved slidingly on a track rail, which is fixed on a mounting base, via a plurality of rolling elements.
2. Description of the Prior Art
There is a conventional linear motion rolling guide unit disclosed in Japanese Patent Laid-Open No. 138428/1993. This linear motion rolling guide unit will now be described with reference to FIGS. 12, 13 and 14.
In this linear motion rolling guide unit, raceway grooves 4 are formed in both of the longitudinal side wall surfaces 3 of a track rail 2, and a slider 1 saddles on the track rail 2 so that the slider 1 can be reciprocatingly moved. The track rail 2 is provided with a plurality of fixing bores 15 spaced from one another in the longitudinal direction thereof as shown in FIG. 14. A mounting base 20, such as a bed, a machine base or a working table for use in fixing the track rail 2 thereon is provided with threads 21. Bolts 16 are inserted into the fixing bores 15 formed in the track rail 2, and the track rail 2 can be fixed to the fixing base 20 by screwing the bolts 16 into the threads 21. Buried plugs 13 are fitted in the upper portions of the fixing bores 15 so that dust and water do not enter the same after the bolts have been inserted into the fixing bores 15.
The slider 1 has a casing 5 movable relatively to the track rail 2 and provided with raceway grooves 9 in the portions thereof which are opposed to the raceway grooves 4 in the track rail 2, a plurality of rolling elements 7, such as balls adapted to roll in the opposed raceway grooves 4, 9, and end caps 6 fixed to both ends of the casing 5. The casing 5 is provided at its upper portion with a plurality of screw holes 19 for use in fixing a slide table (not shown) to the casing 5. The casing 5 and end caps 6 are provided in their lower surfaces with rail inserting recesses 10 so that the casing 5 and end caps 6 straddle and move along the track rail 2. In order to prevent the rolling elements 7 from coming off from the casing 5, retainer bands 18 are fixed to the casing 5 so as to surround the rolling elements 7, and, in order to effect the sealing of clearances between the track rail 2 and the lower end of the casing 5, underseals 8 are attached to the lower surface of the slider 1.
The end caps 6 are provided at both side portions thereof with raceway grooves 22 which form slide surfaces for the rolling elements 7 between the end caps 6 and track rail 2, and direction conversion passages 11 for converting the direction of rolling of the rolling elements 7 for the circulation thereof. Side seals 17 for effecting the sealing of clearances between the track rail 2 and both of the longitudinal end portions of the slider 1 are fixed to the end caps 6, and grease nipples 23 for supplying a lubricant to the slide surfaces between the track rail 2 and slider 1 are provided thereon. The end caps 6 are fixed to both end surfaces of the casing 5 with screws 25 inserted through screw holes 24.
This linear motion rolling guide unit is constructed as described above, in which the slider 1 is placed on the track rail 2 so that the former straddles the latter, the slider 1 sliding freely via the rolling elements 7 circulating along the raceway grooves 4 in the track rail 2. The rolling elements 7 in load regions which roll in the raceway grooves 4 in the track rail 2 are guided into the direction conversion passages 11 formed in the end caps 6, and then moved to return passages 12 formed in the upper portions of the casing 5 so as to extend in parallel with the raceway grooves 9. The rolling elements 7 are thus endlessly circulated in the endless circulating passages. Owing to the rolling of the loaded rolling elements 7 positioned between the raceway grooves 9 formed in the slider 1 and those 4 formed in the track rail 2, the track rail 2 and slider 1 can be moved relatively to each other.
A conventional linear motion rolling guide unit is adapted to reciprocatingly move various types of apparatuses of comparatively large weight over a comparatively long distance with a high accuracy. However, a miniaturized linear motion rolling guide unit for moving various types of miniaturized small-weight apparatuses longitudinally has a track rail of around 5 mm in width, so that the specifications of the track rail-fixing bolts and screws 16 necessarily become not more than M2 (screw diameter of not more than 2 mm). Under the circumstances, it is troublesome to handle the bolts and screws 16, and the strength of the track rail 2 decreases due to the holes made therein for inserting the bolts and screws 16 therethrough.